1. Technical Field
This invention relates to a surface light emitting semiconductor array device, and more specifically, to a stacked layered configuration of a Vertical-Cavity Surface-Emitting Laser diode (hereinafter referred to as VCSEL) array device. This invention also relates to a method for manufacturing the VCSEL array device.
2. Related Art
A VCSEL device is a type of laser diode that emits light from a surface of a semiconductor substrate. VCSELs have excellent characteristics, which edge-emitting type laser diodes do not have. For example, VCSELs require a lower current value for their driving (lower threshold current), and property tests can be performed while VCSELs are on a wafer (nondestructive evaluation), and VCSELs can be easily arranged in two-dimensional arrays. With these characteristics, VCSELs have been used as light sources for an optical data processor or an optical communication device, or a data storage apparatus using light.
FIG. 17 schematically illustrates a configuration of a selective oxidation type VCSEL device disclosed in JP-A-2004-200211. Formed on a substrate 1 are; n-type lower DBR layers 3: p-type upper DBR layers 9: active regions 7 disposed between the upper and lower DBR layers: and a current confining layer 8 that includes an oxidized region 8b being selectively oxidized. A contact layer 10, the upper DBR layers 9, and the current confining layer 8 form a mesa structure on the substrate. An edge portion of an upper surface and a side surface of the mesa structure, and a mesa bottom portion are covered with an interlayer insulating film 13. For the oxidation type VCSEL device disclosed in JP-A-2004-200211, the internal stress of the interlayer insulating film 13 is set to be equal to or less than 1.5×109 (dyne/cm2) in order to prevent release of the mesa structure or the like and extend device life.
An issue of a selective oxidation type VCSEL device is so-called sudden failure. It has been thought that the cause of the sudden failure is that the composition in a stacked layered material alters due to oxidation, which causes dislocations (point defects) in a stacked film. The heat generated by laser oscillation enhances the movements of the dislocations and increases the dislocations, and the dislocations penetrate into an active layer and induce a sudden failure (device degradation). However, further studies have found that the dislocations do not occur simply due to the oxidation, but internal stresses occurred between an oxidized region and an interlayer insulating film formed near the oxidized region is a cause of the sudden failure.
A semiconductor layer that becomes a base of a VCSEL and an interlayer insulating film made of a dielectric film each has a different coefficient of thermal expansion, and thus it is inevitable that stress will occur as temperature rises. Such stress occurrence is especially noticeable in a long array device (that has plural light emitting points) in which stress is easily caused inherently due to warping of the substrate, and such stress occurrence has to be addressed.
An aim of the present invention is to provide a VCSEL device in which life degradation due to stress may be suppressed by controlling the stress that occurs in an interlayer insulating film, thereby the reliability of the device is improved, and provide a method for manufacturing a VCSEL device.